TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3280
SUBJECT: GRB 050416: Swift/UVOT refined analysis
DATE:    05/04/17 00:22:59 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps@mssl.ucl.ac.uk>

P. Schady (MSSL), T. Sakamoto (GSFC/NRC), K. McGowan (MSSL), P. Boyd
(GSFC/UMBC), P. Roming (PSU), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of
the Swift UVOT team.

Starting with the data taken ~207s after the BAT trigger (Sakamoto et al., GCN 
3264) we have co-added the early time data of GRB 050416 in each of the 
Ultra-Violet/Optical Telescope (UVOT) U, B, and V bands. The co-added images 
are made up of 9 x 10s exposures. A source is detected at the position of the 
afterglow (Cenko & Fox, GCN 3265) in the U and B band with magnitudes U = 19.34 
+/- 0.2 and B = 19.85 +/- 0.2. No source is detected in the V co-added 
image down to a 5-sigma limiting magnitude V > 19.57. There is ~173s 
difference between the start of the finding chart exposure, in which a 
source was detected (Schady et al., 3276) and the co-added image.

The magnitudes are based on preliminary zero-points, measured in orbit and will 
require refinement with further calibration.